The invention relates to a throttling-pintle nozzle for fuel injection in an internal-combustion engine having a prechamber engine.
In conventioanl throttling-pintle nozzles the fuel flows out in the pre-injection phase only through the annular gap formed by the pintle and spray hole. The coke layer forming on the surface of the spray hole and pintle during the running of the engine has an adverse effect on the injection characteristic. The accumulation of coke results in a change in shape and sharp reduction of the annular gap. Eventually, an irregular surface of the spray-hole wall results which has an adverse effect on the injection rate of the fuel, the jet form and atomisation of the fuel and consequently on combustion.
To make it possible to overcome these disadvantages effectively, it has already been proposed to prevent the coking up of the passage cross-section, by providing a throttling-pintle nozzle with a flattened portion extending parallel to the longitudinal axis of the throttling pintle (German Unexamined Published Application (DE-OS) No. 28 09 414).
However, even this special passage cross-section fails to ensure injection rates which are fully satisfactory, since even here, because of unavoidable coking, the desired injection rate and the jet form and atomisation cannot be maintained.
An object of the present invention is to provide an improved throttling-pintle nozzle, by means of simple measures, in such a way that it makes it possible to obtain a proportioning cross-section which is less sensitive to coking and which, in the stabilized state, guarantees a good injection rate during prolonged use.
According to preferred embodiments of the invention, a throttling-pintle nozzle arrangement is provided for fuel injection in an internal-combustion engine, especially a prechamber engine of the type including a nozzle needle which lifts off from its needle seat, counter to the direction of flow of the fuel under the pressure of the injected fuel, and the throttling pintle of which is located within a spray hole in the closing position of the nozzle needle. Between the spray hole and pintle, relative to the periphery of the spray hole, there is a passage cross-section for the fuel in the overlap region, which passage is formed by a flattened portion on the pintle extending over the entire length of the pintle. The improvement of the invention comprises configuring the flattened portion of the throttling pintle to extend obliquely relative to the center axis of the pintle, in such a way that the largest passage cross-section is at the mouth of the spray hole, located on the same side as the combustion space.
By utilizing a throttling-pintle nozzle made in accordance with the invention, it is possible to obtain a desired optimum injection rate. This is achieved by appropriately inclining the flattened surface on the throttling pintle. The coking behaviour of the nozzle is markedly improved, since the special passage cross-section increases with an increasing stroke of the needle in the opening direction. A particular advantage is that in the region where the nozzle needle and bore overlap (pre-injection), in view of the coking which is unavoidable in the combustion space, as a result of the inclination of the surface on the one hand an injection rate which starts gently can be obtained. Additionally, the injection quantity can be increased in the region of the overlap, so that the transition from pre-injection to main injection takes place without a sharp break as is preferred in such systems. Substantially more favourable cylinder-pressure characteristics can be achieved, together with improved noise emission characteristics.
Further objects, features, and advantages of the present invention will become more apparent from the following description when taken with the accompanying drawings which show, for purposes of illustration only, an embodiment in accordance with the present invention.